Charles X Gustav of Sweden

Charles X Gustav of Sweden (8 November 1622-13 February 1660) was King of Sweden from 6 June 1654 to 13 February 1660, succeeding Christina and preceding Charles XI. He was the second Wittelsbach king of Sweden, after Christopher of Bavaria in the 15th century, and he enlarged Sweden's empire during the Second Northern War.

Biography
Charles Gustav was born in Nykoping, Sweden in 1622, the son of John Casimir, Count Palatine of Kleeburg and Catherine of Sweden. He learned the art of war under Lennart Torstenson, fighting at the Second Battle of Breitenfeld and the Battle of Jankov during the Thirty Years' War. From 1646 to 1648, he frequented the Swedish court with the goal of wedding his second cousin, Christina of Sweden, but her opposition to wedlock led to her declining his proposal; instead, in 1649, she declared Charles Gustav his successor (in a move opposed by Axel Oxtenstierna and the Privy Council). In 1654, his cousin abdicated, and Charles became King of Sweden.

In 1655, King Charles decided to go to war with Poland-Lithuania, starting the Second Northern War. The Polish voivodeships of Poznan and Kalisz placed themselves under the protection of Sweden after the Swedes easily defeated the Poles, with the Swedes entering Warsaw and occupying Greater Poland. A great number of Polish nobles and their personal armies joined forces with the Swedes, and Charles X captured Krakow after a two-month siege. However, the Poles successfully held the fortress-monastery of Czestochowa, and Charles' cruelty toward the Poles and his inability to work with the Polish nobility led to a nationalist upsurge in the country. In the beginning of 1656, King John II Casimir Vasa of Poland returned from Silesia with a large army, and Brandenburg was convinced to join the war against Sweden to check Charles' ambitions. In January 1656, Charles forced Brandenburg to switch sides, but the Poles waged effective guerrilla warfare, and Russia made peace with Poland and declared war on Sweden that same year. In 1656, Charles' Suedo-Brandenburger army defeated a much larger Polish army at Warsaw, and the Swedes once more destroyed the Polish capital. In 1657, Denmark entered the war against Sweden, but the Swedes dispersed the Danish army and conquered Bremen. Denmark and Poland concluded an alliance against Sweden, but Charles invaded Denmark and made good progress. This ended with a failed siege of Copenhagen in 1659, with the Dutch reinforcing the Danes. In 1660, Charles fell ill with a cold, which evolved into pneumonia as he visited his troops and ignored his illness. He died at Gothenburg in 1660 at the age of 37.